The present invention relates to a deflection apparatus suitable for use in a receiver employing a color cathode-ray tube, for example.
For example, a color cathode-ray tube displays a picture by converging three electron beams emitted from an electron gun through respective predetermined orbits into a deflection center to further deflect the electron beams by using a sawtooth wave signal having a horizontal period and a sawtooth wave signal having a vertical period or the like for scanning the whole screen.
If such deflection of electron beams for scanning is carried out by using simple sawtooth wave signals having horizontal and vertical periods, so-called pincushion and barrel distortions occur in the vertical direction on a scanning line. Therefore, for correcting such distortion in the vertical-direction, a horizontal-deflection current has been modulated in each vertical period, thereby such distortion of a picture being corrected.
However, while the above deflection for scanning is being carried out, horizontal-direction pincushion and barrel distortions occur in a scanning line at upper and lower portions of a picture screen of a cathode-ray tube. Therefore, a picture is corrected in order to cancel such horizontal-direction distortion (referred to as an N/S pincushion distortion).
When such horizontal-direction distortion is electrically corrected, for example, a vertical deflection current is modulated in each horizontal period. Therefore, a general modulating circuit or the like cannot correct such distortion in view of frequency characteristics. As a result, such modulation has been carried out by using a resonant circuit. However, the resonant circuit is applied only to frequencies of a limited number, and hence if the resonant circuit is used for a plurality of frequencies, the resonant circuit must have a complicated arrangement for switching a resonance frequency and so on.
A method of carrying out such correction by attaching a permanent magnet to a deflection yoke is known. If this method is employed, it is impossible to change a correction amount depending upon an individual case. For example, it is impossible to adjust the correction amount in order to correct characteristics which are different depending upon display apparatus. Moreover, it is impossible to adjust the correction amount in response to a condition which a user desires and so on.